Motivated by its importance for microfluidic applications, we study the stability of jets formed
by pressure-driven concentric biphasic flows in cylindrical capillaries. The specificity of this
variant of the classical Rayleigh-Plateau instability is the role of the geometry which imposes
confinement and Poiseuille flow profiles. We experimentally evidence a transition between
situations where the flow takes the form of a jet and regimes where drops are produced. We
describe this as the transition from convective to absolute instability, within a simple linear …

We adress the question of the stability of a confined coflowing jet at low Reynolds number in
various geometries. Our study is motivated by recent experiments in microfluidic devices.
When immiscible fluids flow in microchannels, either monodisperse droplets or parallel flows
are obtained depending upon the flow rate of the aqueous phase and the oil phase. In these
experiments, the confining and the shape of the geometry play a fundamental role. In a
previous paper [Guillot, Phys. Rev. Lett 99, 104502 (2007)], we analyzed the stability of the …